1. Field of the Invention
The field of art to which the claimed invention pertains is solid bed adsorptive separation. More specifically, the claimed invention relates to a process for the separation of methylparaben from a feed mixture comprising methylparaben and wintergreen oil.
2. Description of the Prior Art
Methylparaben (methyl p-hydroxybenzoate) has great commercial utility as a preservative in foods, beverages and cosmetics. An undesirable by-product obtained in the various methods for synthesizing methylparaben is the ortho isomer (methyl o-hydroxybenzoate), known as wintergreen oil. Wintergreen oil is an undesirable contaminant of methylparaben because of its very intense characteristic wintergreen odor, the presence of which is unacceptable for the above uses of methylparaben. Unfortunately, because of the very similar physical properties of methylparaben and wintergreen oil, separation of the two compounds by conventional means, such as fractional crystallization, is very difficult.
It is well known in the separation art that certain crystalline aluminosilicates can be used to separate hydrocarbon species from mixtures thereof. The separation of normal paraffins from branched chain paraffins for example can be accomplished by using a type A zeolite which has pore openings from about 3 to about 5 angstroms. Such a separation process is disclosed in U.S. Pat. Nos. 2,985,589 and 3,201,491. These adsorbents allow a separation based on the physical size differences in the molecules by allowing the smaller or normal hydrocarbons to be passed into the cavities within the zeolitic adsorbent, while excluding the larger or branched chain molecules.
U.S. Pat. Nos. 3,265,750 and 3,510,423 for example disclose processes in which larger pore diameter zeolites such as the type X or type Y structured zeolites can be used to separate olefinic hydrocarbons.
In addition to separating hydrocarbon types, the type X or type Y zeolites have also been employed in processes to separate individual hydrocarbon isomers. In the process described in U.S. Pat. No. 3,114,782, for example, a particular zeolite is used as an adsorbent to separate alkyl-trisubstituted benzene; and in U.S. Pat. No. 3,668,267 a particular zeolite is used to separate specific alkyl-substituted naphthalenes.
In processes described in U.S. Pat. Nos. 3,558,732 and 3,686,342 adsorbents comprising particular zeolites are used to separate para-xylene from feed mixtures comprising para-xylene and at least one other xylene isomer by selectively adsorbing para-xylene over the other xylene isomers. In such processes the adsorbents used are para-xylene selective; para-xylene is selectively adsorbed and recovered as in extract component while the rest of the xylenes and ethylbenzenes are all relatively unadsorbed with respect to para-xylene and are recovered as raffinate components.
In the process described in U.S. Pat. No. 3,917,734 ethylbenzene is recovered in high purity from a feed mixture comprising ethylbenzene and xylene isomers. The process basically comprises contacting the feed mixture with an adsorbent comprising calcium exchanged type X or type Y zeolites, selectively adsorbing the xylene isomers, and thereafter recovering ethylbenzene as a raffinate component.
We have discovered a process with utilizes a type X or type Y zeolite to achieve separation of methylparaben from wintergreen oil.